1. Field of the Invention
The present invention relates to a hollow tubular body having a platinum or platinum alloy hollow tube, suitable for a conduit for molten glass of a glass manufacturing apparatus.
The present invention relates to a glass manufacturing apparatus employing such hollow tubular body.
The present invention relates to a method for heating the hollow tubular body by conduction heating.
2. Discussion of Background
In a glass manufacturing apparatus, a hollow tube made of platinum or a platinum alloy such as a platinum-gold alloy or a platinum-rhodium alloy is employed as a conduit in which molten glass of high-temperature is passed.
In a molten glass feeding apparatus described in JP-A-6-227822 for example, a platinum or platinum alloy pipe is connected to a molten glass outlet located in a lower portion of the glass melting tank. As other examples of the conduit for feeding molten glass, there are a discharge pipe provided to remove impurities from a glass manufacturing apparatus, a discharge pipe for feeding molten glass from a glass manufacturing apparatus to a molding die in order to form an optical element such as lens, prism or the like.
In the glass manufacturing apparatus, the conduit in which molten glass is passed is heated in order to adjust the temperature of the molten glass. There is a case that the conduit is heated from the outside by means of a heat source such as a heater or the like. However, in the case of a platinum or platinum alloy hollow tube, it has been popularly practiced to provide an electrode on the hollow tube to carry out conduction heating.
JP-A-11-349334 discloses a heating device made of platinum usable for a conduit for molten glass. FIG. 5 is a perspective view of the heating device disclosed in JP-A-11-349334. In FIG. 5, reference numeral 100 designates a heating tube of platinum as a heating member, numerals 200a and 200b designate ring electrodes of platinum, and numerals 300a and 300b designate lead-out portions for the electrodes. When the heating device shown in FIG. 5 is used, the electrode lead-out portions 300a, 300b joined to ends of the ring electrodes 200a, 200b are connected to an external power source (not shown), and the heating tube 100 is heated by feeding a current from the external power source.